The use of felts made from asbestos, carbon and graphite using short and straight staple fibers, as well as various ceramic materials, particularly ceramic foams, as thermal insulation having fire blocking properties is generally known. The bulk densities of some of the well known thermal insulating materials are in the range of from 5.6 to 32 kg/m.sup.3 for insulating materials useful at temperatures of up to 1650 degrees Celsius. Even the newest "lightweight" insulating material comprising a ceramic from which a carbonaceous material has been burned out has a bulk density of from 32 to 96 kg/m.sup.3. In addition, with the possible exception of fiberglass which may be used under certain conditions as a fire block, the commonly known thermal insulating materials having fire block properties, such as carbon or graphite felts and ceramic materials, do not have any resiliency, i.e., they do not have the ability to recover from compression (spring back) of the original "loft". Further, these prior art materials are not compressible from their original loft to any great degree since such fibers have little memory.
Both government and industry have conducted extensive research into developing structures or fabrics that would either be nonflammable or at least retard the propagation of a fire. In conjunction with finding an effective material to act as a fire barrier, consumer considerations require that any such materials to be functional, aesthetically acceptable and reasonably priced.
Unfortunately, past efforts to develop a suitable fire barrier have not been very effective. Thus, even fabrics that will not ignite from, for example, a smoldering cigarette and that are considered to be a class 1 fabrics under the UFAC upholstery fabric classification test, will burn when placed in contact with an open flame. Consequently, this leads to the ignition of an underlying material, such as a cushion or mattress.
So called fire retardant foam coatings for draperies, liners and backcoatings for upholstery, as well as chemical treatments for apparel fabrics, that attempt to provide a fire retardant quality to the fabric are commercially available. Unfortunately, these materials are, at best, self extinguishing only when the source of the flame is removed. If the flame source is not removed, these materials will char, lose their integrity and, most importantly, will not prevent the flame from reaching materials underneath the fabric covering which act as a major source of fuel for the fire.
Other attempts at solving the flammability problem have centered on the use of inherently non-flammable fabrics such as fiberglass which can be used, for example, in draperies. It has been discovered, however, that the glass fibers are self-abrasive in that they rub against each other thereby becoming self-destructing due to such abrasive action. Thus, to reduce abrasive action, hand washing and line drying is, out of necessity, the recommended cleaning procedure for such fabrics. Moreover, the relatively brittle glass fibers tend to break and become very irritating to the skin thus rendering any of the applications of the fabric unsuitable where there is extensive skin contact. Fiberglass fabrics usually also contain flammable sizing binders and/or finishes to provide an aesthetic appearance.
Consequently, there is a need for structures such as fabrics, battings, webs, and the like, which not only provide fire shielding properties, but also are washable, lightweight and can be fabricated into aesthetically acceptable fabrics for home and commercial use.
U.S. Pat. No. 4,588,635 to James C. Donovan discloses a lightweight thermal insulation material which is a blend of spun and drawn, crimped, staple, synthetic polymeric fibers having a diameter of from 3 to 12 microns, and synthetic polymeric staple fibers having a diameter of greater than 12 and up to 50 microns. However, the insulation material is flammable.
U.S. Pat. No. 4,167,604 to William E. Aldrich discloses the use of the crimped hollow polyester filaments in a blend with fowl down (e.g., duck or goose down) in the form of a multiple ply carded web which is treated with a thermosetting resin to form a batting having thermal insulating characteristics. The web, however, does not have fire retarding characteristics.
U.S. Pat. No. 4,321,154 to Francois Ledru relates to a high temperature thermal insulating material comprising insulating material fibers and pyrolytic carbon. To make the insulation lightweight, an expanding agent is utilized that is composed of hollow particles such as microspheres.
European Patent Application Serial No. 0199567, published Oct. 29, 1986, to F. P. Mc Cullough, et al entitled, "Carbonaceous Fibers with Spring-Like Reversible Deflection and Method of Manufacture", discloses non-flammable, carbonaceous fibers that are suitably employed in the structures and fabrics of the present invention.
The carbonaceous fibers, particles or platelets have a carbon content of at least 65% and a LOI value greater than 40, as determined by test method ASTM D 2863-77. The test method is also known as "oxygen index" or "limited oxygen index" (LOI). With this procedure the concentration of oxygen in O.sub.2 /N.sub.2 mixtures is determined at which a vertically mounted specimen is ignited at its upper end and just continues to burn. The size of the specimen is 0.65.times.0.3 cm with a length of from 7 to 15 cm. The LOI value is calculated according to the equation: ##EQU1##
The LOI values of different natural and synthetic fibers are as follows:
______________________________________ Polypropylene 17.4 Polyethylene 17.4 Polystyrene 18.1 Rayon 18.6 Cotton 20.1 Nylon 20.0 Polycarbonate 22.0 Rigid polyvinyl chloride 40.0 Stabilized polyacrylonitrile &gt;40 Graphite 55.0 ______________________________________
The term "stabilized" herein applies to carbonaceous precursor fibers which have been oxidized at a specific temperature, typically less than about 250 degrees Celsius for acrylic fibers. It will be understood that in some instances the fibers are oxidized by chemical oxidants at lower temperatures.
The term "polymeric fibers" used herein includes natural fibers as well as other organic polymeric fibers.
The term "permanent" or "irreversibly heat set" used herein when applied to a linear carbonaceous fiber refers to the fiber being heat treated until it possesses a degree of chemical irreversibility.
All percentages hereinafter referred to are in percent by weight.